Question

say I have the following code:

char[5][5] array;

for(int i =0; i < 5; ++i)
{
   for(int j = 0; j < 5; ++i)
   { 
       array[i][j] = //random char;
   }
}

Would there be a benefit for initializing each row in this array in a separate thread?

Imagine instead of a 5 by 5 array, we have a 10 by 10?
n x n?

Also, this is done once, during application startup.

Answer 1

You’re joking, right?

If not: The answer is certainly no!!!

You’d incur a lot of overhead for putting together enough synchronization to dispatch the work via a message queue, plus knowing all the threads had finished their rows and the arrays were ready. That would far outstrip the time it takes one CPU core to fill 25 bytes with a known value. So for almost any simple initialization like this you do not want to use threads.

Also bear in mind that threads provide concurrency but not speedup on a single core machine. If you have an operation which has to be completed synchronously–like an array initialization–then you’ll only get value by adding a # of threads up to the # of CPU cores available. In theory.

So if you’re on a multi-core system and if what you were putting in each cell took a long time to calculate… then sure, it may be worth exploiting some kind of parallelism. So I like genpfault’s suggestion: write it multithreaded for a multi-core system and time it as an educational exercise just to get a feel for when the crossover of benefit happens…